Calculator



Jan. 29, 1946,v H. G, `MDQwl-:LL 2,393,922 CALCULATOR I Filed June 9,1943 2 Sheets-Sheet 1 Jan. 29, 1946.

CALCULATOR Filed June 9, 1943 2 Sheets-Sheet 2 H. G. McDowELL 2,393,922

Patenteci Jan. 29, 1946 UNITED STATES PATENT OFFICE i CALCULATOR HarveyG. McDowell, Wilmington, Del.

Application June 9, 1943, Serial No. 490,185

3 Claims.

The present invention relates to a calculating device, particularlyadapted for use in papermaking plants in connection with the drying endof a paper-making line.

In the production of paper, a continuous web is delivered from the wetend of the line, to a plurality of driers, so that the wet web israpidly dried as it moves continuously through the apparatus. In thedrying of the paper, there are a number of variable features which mustbe taken into account. In the past, it has been the practice to controllthese variables by the skill and experience of the operators or bycomplicated and involved mathematical calculations, or both.

'Ihe primary object of the present invention is to provide a calculatingdevice which will automatically and expeditiously indicate t the'operator, the relationship between these variable factors and whichwill instruct him, substantially instantaneously, exactly how eachvariable factor under his control should be adjusted for maximumefficiency of the paper-producing apparatus.

Operators skilled in the paper-making art appreciate that apredetermined amount of heat must be applied to a predetermined amountof wet paper web, in order effectively to dry the same. The amount ofheat applied to a moving web is a function of the number of drying rollsin the drying end of the line, the temperatures of the rolls and thespeed of movement of the sheet. As the weight of the sheet increases ordecreases, one or more of these factors must be increased or decreased.Similarly, if the weight remains constant and one or another of thevariables changes, the others, or at least one of them, must becorrespondingly changed. For instance, if the temperature of the rollsis decreased, while' the weight of the web remains confactors can bedetermined, substantially instantaneously, thereby avoiding relianceupon the stant, the speed of movement of the web must be decreased orthe number of rolls employed in the line increased. Similarly, if thenumber of rolls is decreased, for one reason or another, the temperatureof the remaining rolls must be raised or the speed decreased.

When the wet end of the machine is changed from one weight of paper toanother, corresponding adjustments must be made in the number of dryingrolls employed, the temperature to which the rolls are heated, and/orthe speed of movement of the web. As stated above, these adjustmentshave, heretofore, been made as a result of the instinctive skill of theoperator and by mathematical calculation, or both. f

The present invention provides an apparatus whereby the relationshipbetween these variable skill of the operator and entirely eliminatingthe necessity for mathematical calculations.

The invention also provides means for calculating the production rate ofthe mill in tons per hour and tons per twenty-four hours, depending uponthe weight of the paper, its speed of movement through the driers, andthe trim or width of the nished sheet. If the weight of the web and itsspeed ofmovement are known, the calculator of the present inventionvimmediately indicates the production in tons per hour and in tons pertwenty-four hours of finished product, for all possible trim widths,thereby eliminating involved, complicated and laborious calculations.Conversely, if a particular production goal is set, for a particulartrim and weight of paper, the calculator of the present invention willsubstantially instantaneously advise the operator as to the speed ofmovement of the web required to meet this goal. Finally, and withoutmanipulating the calculator, the steam pressure (temperature) and theparticular number of rolls needed in operation in the line to maintainthis production rate may be immediately determined.

Thus, the object of the present invention is to provide a calculatorwhich, by simple adjustment, indicates all possible combinations ofadjustments and variations of the several variable factors involved inthe operation of drying paper.r

Since these variable factors bear a direct ratio or a direct inverseratio to one another, the calculator of lthe present invention has beenbas/ed upon the principle of the slide rule, modified so as to make itcorrespond to the variables in'- volved, whose ratios have -beendetermined-by careful observation and calculation.' These variables andtheir relationship to each other'have been translated into logarithmicscales, yjuxtaposed upon a stationary base or stock and amovable memberor slide. For the sake of convenience, and conservation of space, thedivisions of the scales have been arranged on radii of a circle, spacedapart in degrees and functions of degrees generally corresponding tologarithmic spacings on a straight slide rule. The movable member hassimilar scales thereon, and is mounted for rotation relative to thebase.

A preferred form of the invention is illustrated in the accompanyingdrawings, Ibut it must be understood that the invention is not limitedto the arrangement of parts shown therein and described below, since analmost innite number oi' variations in structure and scales can be sub-lstituted by those skilled in the art, from a consideration of thisdisclosure. All such variations as come within the scope of the appendedclaims are intended to be included.

In the drawings: Figure 1 is a plan view of the calculator of thepresent invention.

Figure 2 is a section on line 2--2 of Figure 1,

and

Figure 3 is a plan viewv of the base or stock, with the rotatable slideremoved.

The calculator comprises a base II! which may be made of any suitablesheet material, such as metal, cardboard, celluloid, synthetic resin orany other plastic. The base carries a stud II, upon which the slide ormovable member I2, made of similar sheet material, is mounted forrotation.

The -base is provided with a plurality of scales arranged on concentricarcs, all struck about the center of the stud II and each having theindividual markings thereof spaced varying distances from one end, inaccordance with the principle of the well known logarithmic scales usedin slide rules.

For purposes of making` the calculations described above, these scalesmay include a scale I5, having numerals associated with the variousmarkings to indicate the speed of travel of the paper web in units of100 feet per minute, as indicated by the legend I6 adjacent the scale. Asimilar logarithmic scale I1, which may be spaced radially outwardlywith respect t the scale I6, may have markings to indicate tons of paperproduced per hour, and an appropriate legend I8 may be associatedtherewith.

A third scale I9, preferably positioned radially inwardly of the scale Iand opposite the scale Il, may be marked to indicate various numbers ofhundreds o-f tons of paper produced per twenty-four hours, as indicatedby the legend 20. The fourth scale 2I, comprising elongated radial lines22, spaced apart in a similar manner, according to the logarithmic scaleprinciple, indicates various numbers of drying rolls employed, fromfifty to one hundred, the legend 23 for this scale, however, beingpositioned upon the rotatable slide I2. The radial lines 22 of the scale2|, for purposes hereinafter described, are intersected Iby a pluralityof arcs 2529, both inclusive, adapted to co-nstitute continuations ofsimilarly positioned arcs 25a-29a, both inclusive, on the rotatableslide I2 and each leading to an indicia 30 for a particular steampressure, as indicated by the legend 3| on the rotatable slide.

The rotatable slide l 2 preferably takes the form of a disc made of anysuitable sheet material, preferably corresponding to that of the base,and having arcuate peripheral edges 35, 36 struck about the center II,but spaced dierent distances therefrom and connected to each other byangular edges 31, 38. The disc also has two arcuate openings or windows40, 4I formed therein, in order to expose the scales I9 and 2I,respectively. The opening 40 is in the form of an elongated concentricarcuate slot, while the opening 4I has one end defined by concentricarcs and another, pointed end defined by an angularly disposed and anarcuate margin, for purposes hereinafter explained.

The upper portion of the disc, in the space between the cut-outl and theouter margin 36 is provided with a logarithmic scale I5 having numerals46 corresponding to various widths of trimmed paper in inches, which maybeproduced in the mill from one hundred and fifty to two hundred andthirty inches. as indicated by the legend 41. It should be noted thatthe markings in this scale are the same on both edges and that they areadapted to register with the scales I1 and I9, respectively, indicatingthe production in tons per hour and in hundreds of tons per twenty-fourhours.

The arcuate margin Il of the disc I2 is provided with a scale 5l, havingnumerals II associated therewith, indicating various weights of paperproduced in the mill, by the conventional designation of weight per onethousand square feet, as indicated by the legend 5l. The mark ings onthe scale 5I are positioned adjacent to and are adapted to register withthe markings on the scale I5, indicating the speed of travel of thepaper sheet per minute in units of one hundred feet.

As stated above, the disc I2 also carries a column of figures 30 forvarious roll temperatures, translated into the more convenient form ofsteam pressure in pounds per square inch, and arcuate lines 25a-28a leadfrom these numbers toward the radial lines 22 associated with the dryingroll scale 2I. The expedient shown has been adopted for convenience, inplace of having the steam pressure or temperature scale arranged alongan arcuate curve, in a manner similar to the other scales, but it willbe noted that each line 25a-29a terminates on the straight angular edge55 of the opening II at a point disposed on a radius spacedcircumferentially from the next adjacent radius in accordance with thespacing of a logarithmic scale. Hence, when any particular point ofintersection between a line 25a-29a and the margin 55 is brought intoregistration with a radial line 22, corresponding to a particular numberof operative drying rolls, the disc is adjusted with respect to the basein the same manner as if an arcuate scale along an inner or outer marginof the cut-out 4I had been provided.

The outer margin of the cut-out 4I is disposed upon concentric inner andouter arcs 56, 51, connected by a straight, angular edge 5B, havingindicia 59 disposed therealons, representing various efficiencies, ashereinafter explained and as indicated by the legend 60.

It will be noted that the scales for the different variable factorswhich have a direct relation to each other are disposed in juxtapositionon the base I0 and the rotatable disc I2. The production in tons perhour and in hundreds of tons per twenty-four hours obviously dependsupon the width of the paper sheet. Hence, the scale 45, indicating trimin inches, is positioned to register with the production rate in tonsand hundreds of tons. As a result, for any particular setting of therotatable disc, corresponding to a particular combination of speed oftravel and paper weight, it is possible to read, adjacent the illurecorresponding to the trim being produced, the rate of production in tonsper hour and hundreds of tons per twenty-four hours.

Similarly, the weight of the paper and the speed of movement of thesheet are in inverse ratio, when the steam pressure and number of rollsare held constant. Therefore, all combinations of weights and speeds maybe read at a glance, by comparing the markings on the weight scale 50with the markings on the speed scale I5.

The number of drying rolls and the temperature of the rolls similarlyare in inverse ratio, since as the number of rolls is decreased, thetemperature must be increased. Hence, the temperaturev scale, lprovidedby the vpoints of junction o! the lines 29d-29a with the margin l. ofthe opening II, is positioned to register withthe scale :I for thenumber of drying rolls. For any setting of the rotatable slide, it is,thereforefpgssible to read all combinations oi drying. temperatures orsteam pressures and numbers oi' drying rolls.

The manner in which the various scales were computed and laid out willbe briefly described. The divisions oi' the various scales are similarto logarithmic scales on a slide rule, except that they are measured indegrees of a circle instead of in inches. For example, in each oi' thescales I9 and I1, the graduation marked 2 is placed at 30.1, from animaginary starting point, since the logarithm of 2 is 301. Similarly,the graduation marked 3 is placed at 47.7, corresponding to thelogarithmic 477 for the number 3. However, since the spacing of thedivision and sub-division lines would be quite minute in certaininstancesall of the degrees have been multiplied by 3.

The markings in the scale 2| for 50 to 100 driers, both inclusive,correspond to the logarithmic values, as indicated by a particular steampressure. 'This value is directly proportional to the number of driersemployed, since 100 driers have twice the drying capacity of 50 driers.

The value of the driers is known as the drying rate or the amount ofpaper which can be dried per hour, per square foot of drying surface.Applicant has determined, from experiments conducted and data collectedin the past, that the drying yrate is equal to the temperature inFahrenheit degrees multiplied by .0112 minus 1.708. Since the totalsurface of one 60 inch diameter drier for a trim of one inch is 1.308square feet, the capacity of a roll in tons per h our equals the dryingrate multiplied by 1.308, multiplied by the trim, divided by 2,000,l thenumber of pounds per ton.

The angle of the margin 55 was determined by calculating the number ofdriers required to dry an equivalent amount of paper at 50 pounds steampressure and at 25 pounds steam-pressure, the intermediate pressures andnumber of rolls being in direct proportion. For example, a straightline, as indicated at 62 in Figure 3, starting at 50 driers on the 50pound circular arc would terminate at 63.4 driers on the 25 pound arcbecause the ratio based on the comparative drying rate is 1.268 and thesame ratio prevails for any other combination. This angular cut is usedin lieu of a series of lines, similar to line 62, which would otherwisebe required on the scale 2i.

The indicia 6-25 'associated with the tons per hours" scale I1 have anindex value of one, but the numbers below vsix have been omitted sincethe range, 6 to 25 tons, represent the extreme limits of production perhour, when the other factors of the scale are considered. The markingsin the scale I9, indicating tons per twenty-four hours in hundreds, havea 4proportional value, so that any reading on the scale I9 istwenty-,four

. times the corresponding reading on the scale I1.

The tonnage produced is the product obtained f by multiplying theimplied value, obtained from the scale 2l for the number of driers, bythe trim, yindicated on the trim scale I5. This muldicated by the radiallines 22.

'nie muon :or any mm n round in me scala i1 opposite the number in thescale Il for the particular trim under consideration. The productrepresents the addition of the logarithms of the numbers correspondingto the implied value of the driers and the indicated trim. Theproduction in hundreds of tons per twenty-four oi trim is to 230 inches,corresponding to 1.5 to 2.3 on the logarithmic scale.

'I'he weight scale 59 is a reverse scale, since the speed of travel ofthe web, indicated by the speed scale I5, is inversely proportionate. Itwas simpler to make the scale l0 a reverse scale, although, obviously,the opposite arrangement could be adopted, i. e. making the scale I! areverse scale and the scale 50 a normal one. The index value ofthe scale50 is 10. but only the portion between 23 and 90 is included, sincethese gures represent the limits of paper weights in a Fourdrinier kraftboard mill of the type with which the embodiment of the invention shownin the accompanying drawings is adapted to be us'ed.

The speed scale I5 has an index value of one, but the index is omittedfor similar reasons. The scale was developed directly from the scale 2|for the number of driers and the scale 50 for the weight of paper,excluding the production rate scales Il and I9 and the trim scale 45because the implied tonnage of the scale 2| is on the basis of one drierper one inch trim. This value multiplied by the number of driers,multiplied by the factor 200, divided by the sheet weight gives thespeed in feet per minute.

The relative positions of the scales I5, Il and 2| on the base I0 areunimportant and have been selected for convenience and for evendistribution of the lgures over the base. The scale I9 must be inpredetermined relation to the scale Il, since the figures in the scaleI9 correspond to a multiple of those in scale I1. In other words, eachfigure in scale I9 corresponds to the ligure in scale I'I, radiallyaligned therewith, when multiplied by 24. e

'I'he relation of the scales 45, 50 and 55 to the scales on the base andto each other are of vital importance, once the scales on the base havebeen positioned in the arbitrarily selected relation to each other. Therelative positions of the scales on the slide or disc I2 are determinedby working out one or more specific problems, in accordance with theprinciplesand the formula explained below. When these scales have beenso positioned in accordance with one or more specific examples, thegures will be accurate for all other combinations of temperatures,numbers of dryers, speeds of movement, weights of paper, trim andproduction in tons per hour and hundreds of tons per 24 hours.

Obviously, the reverse procedure in laying out the scales could beadopted. That is vto say. the scales could ilrst be marked oi on thedisc. and then applied to the base, by plotting the results of one ormore mathematical computations.

The multiplication and division is mechanically performed simultaneouslywith the setting of the revolving, disc for ascertaining the tonnage, asexplained above. The speed of movement of the sheet is found on thescale I5 opposite the indicia on the scale 50, corresponding t0 theselected sheet weight. Also available, without moving the revolvingdisc, is the corresponding speed for any sheet weight from 23 to 90pounds.

The efficiency scale on the angular edge 58 of the window 4l is usefulbecause the calculations of the other scales have been predicated upon100% efficiency in operation and many driers do not come up to thisstandard. The figures on this scale are spaced apart as in a logarithmicscale and therefore automatically indicate the designated percentages.This logarithmic scale has numerals associated with the percentagesindicated thereon. The marking l is located in respect to chart 2l sothat it will register initially with the minimum number of driers, whichis fifty, when that number of dryers registers with the minimum steampressure, which is twentylive pounds. When the radial line representingthe number of driers selected coincides with the figure 500 in the scale55, the efficiency is 100%. The figures 90 and 80 are for the purpose ofcomparing the performance of existing paper machines with the valuesestablished for the production calculator. For example, if a machinewith sixty driers and 25 pounds steam pressure is producing 6.79 tons ofpaper per hour for a trim of 150 inches, the 100% emciency gurecoincides with the radial line for fifty-four driers and the sixty drierradial line coincides with the 90% eciency figure. Hence, the efficiencyis 90%. Also, if the same machine without reference to the tonnage isoperating at a Speed of 80 feet per minute for a 3G pound sheet, thedrier radial line (100% efficiency) coincides with 80. Therefore, theeiciency is 80%. The equivalent speed for 100% efficiency would be 600feet.

The angular cut, adjacent the eticiency figure, has no particularsignificance, except that it permits more of the 50 pound circular arcto be visible than would have been the case, had the figures been placedon the periphery of the circle.

t is thought that the operation of the calculator of the presentinvention will be entirely clear to those skilled in the art from aconsideration of the foregoing description. For instance, if it isdesired to find the production of hours and the speed of movement of thesheet, when the number of driers and steam pressure are known, it issimply necessary to revolve the disc l2 until the line 25a-29a leadingfrom the steam pressure intersects the line 22 corresponding to thenumber of driers employed. Adjacent to the scale 45 marked trim" will befound the production per hour on the scale il and per tweny-four hourson the scale i9. Adjacent the figure on the weight scale 50corresponding to the paper being produced will be found, on the speedscale i5, the figure corresponding to the speed of movement of the paperin feet per minute.

Conversely, when it is desired to find the number of driers and steampressure required, when the production in tons and the trim are known,it is necessary simply to revolve the disc until the known productionand trim coincide. All possible combinations of numbers of driers andsteam pressures are indicated by the points of intersection between thevarious lines 25a- 29a and the lines 22.

If it is desired to find that alternate speeds for various sheetweights, when the speed for a deflnite sheet weight is known, the discis rotated until figures for the known speed and sheet weight coincide.Opposite any weight on the scale 50 paper in tons per hour or tons pertwenty-four will be found the corresponding speed, in the scale IB, lnfeet per minute. In a similar manner, it is possible to read from thespeed scale back to the weight scale, to determine various weights ofpaper that may be produced at different speeds, using any particularcombination of temperature and number of driers.

If it is desired to find the eiiiciency when the production, trim andnumber of driers are known, the disc should be revolved until the trimand production selected coincide. Adjacent the number of driers actuallyemployed will be found the efficiency in percent.

Similarly, the efficiency may be determined. if the sheet weight, speedand number of driers are known. This is accomplished by revolving a discuntil the sheet weight and speed coincide. Adjacent the number of drierswill be found the efiiciency in percent.

As illustrating the simplicity of calculation with the device of thepresent invention, as compared with mathematical calculations heretoforeemployed, a typical mathematical calculation will be explained. Toobtain the figure for the tons per hour produced, for a known steampressure, number of driers and trim, it is necessary to calculate thedrying rate, as explained above, by multiplying the temperature times.0112, minus 1.708. The drier surface must also be computed, bymultiplying the number of driers by 1.308 and multiplying the product bythe trim in inches. In order to calculate the tons per hour, the dryingrate must be multiplied by the drier surface and the product divided by2,000 (pounds per ton).

As explained above, these complicated calculations may be performedmechanically, by the use of the instrument of the present invention by asimple manipulation of the slide, to bring the steam pressure and numberof driers into registration. The production may be read on the scale Il, opposite the figure for the trim in inches.

The fundamental equation showing the relationship between variousfactors involved in this device may be expressed as follows:

PSNXSXRX T 2,000 in which P=production in tons per hour,

N=the number of dryers,

S=l.308 (surface in square feet of one dryer for each inch of trim),

R=the drying rate (temperature) (M12-1.708),

T=the width of the trimmed sheet in inches, and

2,000 stands for pounds per ton.

If we have the problem of determining the production in tons per hour ofa paper machine having fifty dryers, each 60 inches in diameter, withfifty pounds steam pressure per square inch therein (temperature 297.7F.) and 150 inchtrim, the problem would be worked as follows:

50X 1.308X 1.6262X 150 The dliliculties in performing themultiplications and division required in solving this problem areobvious. To solve the same problem by the calculator of the presentinvention, the fifty pound steam pressure on scale 55 is set to coincidewith the 50 dryer ngure in scale 2|. By reading the number in scale Hopposite the indicia corresponding to l 50 in the trim scale 4l, theanswer is found. Without changing the setting of the disc, theproduction in 24 hours may be determined, by reading the figure in thescale I9, opposite the |50 trim ilgure.

Another formula showing the relation between the speed of movement ofthe sheet in 100 feet per minute, the weight of the paper, per 1,000square feet, and the tons per hour and trim in inches may-be expressedas follows:

S=speed per minute in 100 feet,

2,000=pounds per ton,

K a constant=200 for 1,000 square feet basis, W-:weight of sheet inpounds per square feet, and T=trim in inches.

The mathematical calculations required to reduce this formula aresomewhat involved, but they may be automatically performed by simplysetting one pair of known figures in the problem, whereupon the unknownmay be read opposite the third known quantity. For instance, ii' thetrim and the paper weight are known, as well as the speed in feet perminute, the production gures per hour or 24 hours may be determined byadjusting the weight and speed gures and reading the production oppositethe number trim. Similarly, if a predetermined production schedule mustbe met, for a known weight and trim of Paper, the speed may bedetermined by adjusting the production rate (tons per hour) and the trimto correspond, whereupon the speed in 100 feet per minute may bedetermined by reading the figure in the scale i opposite to the knownweight in scale 50.

It must be understood that the invention is not limited to the detailsof construction shown in the accompanying drawings and described above,since the principles of invention may be embodied in many modifiedforms. All devices coming within the scope of the appended claims andtheir equivalents are intended to be included.

I claim:

l. A calculator for solving problems in the manufacture'of paperinvolving variables relating to rate of production in weight, number ofdriers. temperature of driers, width of paper and speed of movement oi.'the sheet, having the relation expressed by the formula p N XS X R X T2,000 in which R=the drying rate (temperature in degrees Fahr-` enheitX.01121.708), T=the width of the trimmed sheet in inches, and2,000=pounds per ton,

said calculator comprising a base having logarithmic scales arranged onarcs of progressively larger concentric circles, the innermost scalecorresponding to numbers of driers, the next outer scale correspondingto speeds of movement of the sheet. and the outermost scalecorresponding to rates of production in tons per unit of time, and aslide mounted for rotation on the center of said concentric circles andhaving margins registering with the scales on the base and logarithmicscales along said margins corresponding respectively with thetemperatures or steam pressures of the rolls, the weights of the paperand the trim of the paper, the scales being so arranged that, for asetting of any one pair of variables represented by a scale on the baseand the adjacent scale on the slide, a plurality of other correspondingpairs oi variables are indicated in the two other sets of scales on thebase and slide, respectively, the slide having a lgenerally arcuateopening therein, exposing the in nermost, number oi.' driers. scale onthe base, said opening being dened at one end by a straight line margindisposed at an oblique angle to a radius of the slide, the temperatureor steam pressure scale being arranged along said straight line marginin position to register with the number of driers scale therebelow.

2. A calculator for solving problems in the manufacture of paperinvolving variables relating to rate of production in weight, number ofdriers, temperature of driers, width of paper and speed of movement ofthe sheet, having the relation expressed by the formula in whichP=production in tons per hour,

N=the number of driers,

S=.1308 (surface in square feet of each 60 inch drier for each inch oftrim),

R=the drying rate (temperature in degrees Fahrenheitx .M12-1.708),

T=the width of the trimmed sheet in inches, and

2,000=pounds per ton,

said calculator comprising a base having logarithmic scales arranged onarcs of progressively larger concentric circles, the innermost scalecorresponding to numbers of driers, the next outer scale correspondingto speeds of movement of the sheet, and the outermost scalecorresponding to rates of production in tons per unit of time, and aslide mounted for rotation on the center of said concentric circles andhaving margins registering with the scales on the base and logarithmicscales along said margins corresponding respectively with thetemperatures or steam pressures of the rolls, the weights of the paperand the trim of the paper, the scales being so arranged that, for asetting of any one pair of variables represented by a scale on the baseand the adjacent scale on the slide, a plurality of other correspondingpairs of variables are indicated in the two other sets of scales on thebase and slide, respectively, the slide having a generally arcuateopening therein exposing the innermost number of driers scale on thebase, the scale for temperature or steam pressure being arranged along amargin of said opening in position to register with the number of driersscale therebelow.

3. A calculator for solving problems in the manufacture of paperinvolving variables relating to rate of production in weight, number ofdriers, temperature of driers, width of paper and speed of movement ofthe sheet, having the relation expressed by the formula P: NX S X RX T2,000 in which P=production in tons per hour,

N :the number of driers,

82.1308 (surface in square feet of each 60 inch drier for each inch oftrim),

R=the drying rate (temperature in degrees Fahrenheit .01121.708)

T=the width of the trimmed sheet in inches, and

2,000=pounds per ton,

said calculator comprising a base having logarithmic scales arranged onarcs of'progressively larger concentric circles, the innermost scalecorresponding to numbers of driers, the next outer scale correspondingto speeds of movement oi the sheet, and the outermost scalecorresponding to rates of production in tons per unit of time, and aslide mounted for rotation on the center of said concentric circles andhaving margins registering with the scales on the base and logarithmicscales along said margins corresponding respectively With thetemperatures or steam pressures of the rolls, the weights of the paperand the trim of the paper, the scales being so arranged that, for asetting of any one pair of variables represented by a scale on the baseand the adjacent scale on the slide, a plurality ot other correspondingpairs ot variables are indicated in the two other sets of scales on thebase and slide, respectively, the slide having a generally arcuateopening therein exposing the innermost number of driers scale on thebase, the scale for temperature or steam pressure being arranged along amargin of said opening in position to register with the number of driersscale therebelow, the slide having other outer margins disposed on arcsof concentric circles, with the weight scale along the margin of lessradius in position to register with the speed of movement scale, and thetrim scale along the margin of greater radius in position to registerwith the rate of production scale HARVEY G. MCDOWELL.

